• Community:
  • small scale: decomposers on a fallen log
  • large scale: flowers + pollinators in Shenandoah national park

• Interactions can help, harm or have no effect

• Outcome of interactions determine which species are present

• Sum of interactions determine how an ecosystem functions
  • productivity, water quality, population control

• Individuals sharing space will compete for resources
  • reduces fitness for each species

• Resources can mean many things:
  • prey items, water, nutrients, space

• Competitive exclusion:
  • local extinction
  • rare in nature (sometimes on islands)

• Ecological niche:
  • abiotic factors, food choice, nest sites
  • competition occurs for these resources

• Natural selection reduces overlap between niches!
  • resource partitioning: division of limited resources

• Resource division allows for coexistence
  • use parts of a habitat, active at different times
  • allows partial niche overlap (not full)
  • why competitive exclusion is rare!

• Review: all animals are heterotrophic….

• All animals must eat, which means that most organisms are also at the risk of being eaten

• Exploitation: species feeding interactions (+/-)
  • predation, herbivory & parasitism
  • the drama drives natural selection!

• One species (predator) kills and eats other (prey)

• Lots of feeding adaptations in the animal world
  • fangs, claws, echo-location, venom, etc. etc. etc.

• Fitness (reproductive success) depends on feeding

• Not getting eaten is just as important as eating
  • powerful driver of natural selection

• Behavioral adaptations
  • hiding, fleeing, herding
  • active self defense less common

• Morphological adaptations
  • spines, odors, toxin accumulation
  • mimicry and camouflage

• Organism (herbivore) eats part of plant or alga
  • harms the plant

• Herbivores are large & small, terrestrial & aquatic

• Like predators, many special adaptations
  • chemical sensors to identify toxins
  • specialized teeth or digestive systems

• Review: Plants don’t move
  • just as many defensive adaptations
  • thorns, toxins, etc.

• Positive interactions occur where one at least one species benefits and their other is not harmed

• Positive interactions common in ecological communities
  • drive higher biodiversity

• Mutualism and commensalism are the most common

• Occur when both species benefit from the interaction
  • common in nature

• Often, the 2 species depend on each other for survival/reproduction
  • plants + insects = pollination + food

• Usually still a cost, but benefit > costs
  • carbon - nitrogen trade-off between plants and fungi

• Commensalisms are interactions where one benefits but doesn’t harm/help the other
  • also common in nature

• Some biologists argue that any close interaction between two organisms is unlikely to be completely neutral for either party
  • especially over time

• Structure and dynamics of a community depend on feeding relationships

• Energy is transferred upward
  • plants/aglae → consumers
  • transfer is wasteful (most energy is lost)

• Trophic level:
  • many species can share a trophic level

• Structure and dynamics of a community depend on feeding relationships

• Energy is transferred upward
  • plants → consumers
  • transfer is wasteful (WHY?)

• Exists in terrestrial and aquatic systems
  • What happens if a species goes extinct?

• Dominant species:
  • better @ obtaining resources
  • defense wins championships

• Keystone Species:

• Ecosystem engineers:
  • impact every community member